1. Field of the Invention
This invention relates in general to oil and gas well downhole equipment, and in particular to an actuator that is remotely actuated by fluid pressure applied from the surface.
2. Description of the Prior Art
In an oil and gas well, at times, a downhole mechanism must be remotely actuated. For example, a test tool may be lowered on tubing and located in the vicinity of a formation for which testing is desired. The formation is isolated from the well annulus by setting a packer between the tubing and the well bore or casing. A valve in the test tool must be opened to allow fluid to flow from the formation being tested into the tubing. This is handled in various ways.
In one technique, an actuator will be incorporated with the test tool. The actuator has an actuating element that moves the valve in the test tool. The actuating element will be moved by increasing the annulus pressure surrounding the tubing and the actuator. This is handled by applying pressure at the surface, with the annulus being filled with fluid.
While this is workable, improvements are desirable. For example, the tool must be sized so that the annulus pressure due to hydrostatic force does not actuate the tool while being run to operating depth. Also, these tools normally utilize closed chambers filled with fluid. Increasing temperatures encountered as the tool descends into the well will cause the volume of the fluid to expand. To avoid premature actuation, this must be accounted for, making the equipment complex.
In another instance, safety valves will be located downhole in producing wells. A safety valve will be located in the production tubing. It has a spring that urges the valve to a closed position. An actuator will be connected to a control line that extends through the annulus to the surface. The operator applies hydraulic pressure to the control line to cause the actuator to move the valve against the spring to the open position.
While this type of safety valve is workable, large springs must be used so as to prevent the hydrostatic pressure in the control line from causing the safety valve to open. Consequently, the depth to which the safety valve may be run is limited by the size of the spring which can be incorporated in the tool. The safety valve protects against damage causing loss of pressure in the control line running from the valve to the surface. If the well head is blown away during a storm, the control line would be broken and pressure would be lost (except for hydrostatic) and the valve would close, thus preventing uncontrolled flow. Thus the greater the depth, the greater the protection.